It was always easy to underestimate Dieter Bock: the clothes from C&A; the plastic carrier bag instead of a briefcase; preferring public transport to chauffeured limousines; drinking Château Petrus with pasta. Many made that mistake, helping the publicity-shy German tax lawyer to build a fortune estimated at £500m by the time of his death at the age of 71.

No one misjudged Bock's abilities and ambitions more than the Lonrho tycoon, Tiny Rowland. He invited Bock in as a saviour. But the corporate son became his nemesis, forcing Rowland out of the Africa-wide company he had dominated for three decades. Lonrho needed cash, and Rowland, at the age of 75, a lucrative exit strategy. Working, as usual, with other people's money – a German bank loan – Bock became the conglomerate's biggest shareholder in December 1992, paying Rowland £50m for the privilege, and joining the board in February 1993.

But within months, the "indivisible" joint chief executives were at war. Bock, tearing up the Rowland script, forced through the prized asset sales – including the Observer to the Guardian Media Group in 1993. In March 1995 Rowland was sacked by his handpicked board, which was now backing Bock. Bock sold out to the mining firm Anglo American Corporation for a £123m profit in October 1996, leaving Lonrho in March 1997.

Bock was born in Dessau, eastern Germany. His family fled to the west in 1953, settling in Munich. His father ran a film materials business. Bock qualified as a lawyer and then an accountant before setting up as a tax adviser in 1973. Looking for offices to rent, he instead persuaded his would-be landlords to sell the building cheaply. That deal, in 1974, launched Bock into property.

He then went on to become what some saw as a virtuoso for wealthy customers, including some of the richest German families. He was described as silent, rich and opaque, a master of entrepreneurial complexity. He was amiable and charming to some, coldly calculating and an unscrupulous speculator to others.

Bock rode the property boom, expanding into the Netherlands, the US and South Africa. He became a significant investor in the leading construction group Philipp Holzmann and the largest shareholder in the Kempinski hotel chain.

In the early 1990s he came shopping for opportunities in the bombed-out British market. Lonrho's shares were depressed by its debt burden. Bock saw that he could buy valuable assets cheaply while Rowland, whose father was German, thought he saw a man he could control.

Bock paid way over the market price for half of Rowland's Lonrho shares and £85m for new shares. Although he had borrowed the money and was paying Rowland by instalments, Bock was presented as a billionaire.

An adviser on the Lonrho deal described Bock as "academic, like a university don, very quiet. You could see him thinking. He would say very little but when he spoke, he was very precise. Everything was inside his head. He was a single player, no big operation."

Deferential or determined as required, Bock was on one occasion reminded not to sit in Rowland's chair at a Lonrho lunch, and promptly moved. He came across as secretive, verging on evasive, giving nothing away.

The Lonrho shares were acquired through a Dutch company, Laerstate. Another Dutch company owned his London flat. Rowland remarked: "Mr Bock doesn't own a single asset in his own name, except his bicycle – and perhaps his wife."

Faced with Bock's determination to cut costs, Rowland ended his £25m legal feud with another former ally, Mohamed Al Fayed, over the 1985 Harrods takeover. The two enemies appeared smiling in the Harrods food hall alongside a stuffed white shark named Tiny, devouring a smaller shark named Bock.

But Bock had the last laugh. A year after forcing Rowland out, Bock surprised his adversary again, buying out the remainder of his Lonrho stake for £91m, then immediately selling on to Anglo American. He manoeuvred Anglo into buying his shares at well above the market price for £258m.

Though he was a smart negotiator, conflict and litigation appeared to follow Bock. A modern art lover – yachting was his other passion – he provided more than £1m for the purchase of paintings by the Frankfurt Museum of Modern Art. But after 15 years, in 2005 he reportedly suddenly removed 500 works bought with his money. Selling just three of these recovered his original payment. He backed the Museum of the Imagination in Munich, but then sold the by then empty building after falling out with those involved.

Despite, according to a former business partner, having no interest in football, he acquired a soccer team in Soweto, South Africa, the Moroka Swallows, in 2001. But Bock was no hero to the fans, who welcomed his decision to sell last March.

By 2005 there were reports that the Bock empire was under financial pressure, although he remained an investor in some of Germany's most prestigious hotels.

After he was forced out, Rowland promised to pursue Bock "until the end of my days" – and beyond. In 2002 his estate won a £250,000 claim for unpaid commission against Bock. The claim had been acquired by Rowland for £1 from the man who had introduced them. Bock's evidence was rejected by a High Court judge as insincere, indicative of his "manipulative powers and temperament".

The Rowland legacy struck again last July when HM Revenue & Customs won a ruling that Laerstate was resident in Britain, and so liable for corporation tax on the Lonrho shares profit – a potential bill of £40m plus interest. The tribunal expressed concern that Bock's appeal against tax assessments made in 1997 had not started for 10 years. It rejected his evidence that Laerstate had been run by a Dutch associate from the Netherlands, and not by him from London. An appeal is pending.

Bock's death mirrored his life, shrouded in mystery. He choked to death on a piece of steak at one of his hotels, the Atlantic in Hamburg. Although he died on 12 May, his death was not announced until the funeral, two weeks later. The Atlantic was a location in the 1997 James Bond film Tomorrow Never Dies, about a media mogul who wanted world domination.

Bock is survived by his wife, Olga, and four sons.

• Hans-Dieter Bock, lawyer and tax consultant, born 3 March 1939; died 12 May 2010